Thanks Simon! Yes, that's quite helpful, actually. I'm quite happy with the default Sony app. What tempts me with Morkl's modified reader are, of course, the fonts and font-size options. (Also, can you add custom css, and if so, how? That's not clear to me.)
But I'm a big chicken when it comes to messing with firmware. Every time I start reading threads about rooting and tinkering, most of it goes over my head, plus it generally requires a PC which is foreign territory for me, so I freak out.
Maybe I'll wait a little while and see if Morkl posts an update, just to be make extra sure everything works if I attempt this ...